Congenital anomalies are the second leading cause of perinatal mortality in the United States after premature birth. Advances in imaging techniques have allowed the detection of many anatomical defects with ultrasound before birth. The goal of this project is to improve the diagnosis and treatment of fetal disease and congenital anomalies. The Perinatology Research Branch has initiated a project to use tri-dimensional ultrasound to delineate normal fetal anatomy, improve the detection of congenital anomalies and the estimation of fetal weight and growth. The Branch has acquired the skills and equipment to initiate the project. The diagnostic power of this technology is illustrated by the improved detection of a vassa previa, a rare but potentially lethal condition. This condition is characterized by the presence of aberrant fetal vessels within the fetal membranes in close proximity to the uterine cervix. At the time of rupture of membranes (spontaneous or artificial), patients with a vassa previa may sustain laceration of the fetal vessels resulting in fetal exsanguination and fetal death or severe anemia and neurologic handicap. Therefore, prenatal diagnosis is critical. The Branch has been able to use grey scale multi-planar and the "flight path" techniques to make the diagnosis in two cases. We expect that tri-dimensional ultrasound would enhance the precision of prenatal diagnosis of many other congenital anomalies.